1. Field of the Invention
The present invention relates to fluidic dispensing devices, and, more particularly, to a fluidic dispensing device, such as a microfluidic dispensing device that carries a fluid for ejection, and having a multi-tier stir bar for mixing the fluid in the fluidic dispensing device.
2. Description of the Related Art
One type of microfluidic dispensing device, such as an ink jet printhead, is designed to include a capillary member, such as foam or felt, to control backpressure. In this type of printhead, the only free fluid is present between a filter and the ejection device. If settling or separation of the fluid occurs, it is almost impossible to re-mix the fluid contained in the capillary member.
Another type of printhead is referred to in the art as a free fluid style printhead, which has a movable wall that is spring loaded to maintain backpressure at the nozzles of the printhead. One type of spring loaded movable wall uses a deformable deflection bladder to create the spring and wall in a single piece. An early printhead design by Hewlett-Packard Company used a circular deformable rubber part in the form of a thimble shaped bladder positioned between a lid and a body that contained ink. The deflection of the thimble shaped bladder collapsed on itself. The thimble shaped bladder maintained backpressure by deforming the bladder material as ink was delivered to the printhead chip.
In a fluid tank where separation of fluids and particulate may occur, it is desirable to provide a mixing of the fluid. For example, particulate in pigmented fluids tend to settle depending on particle size, specific gravity differences, and fluid viscosity. U.S. Patent Application Publication No. 2006/0268080 discloses a system having an ink tank located remotely from the fluid ejection device, wherein the ink tank contains a magnetic rotor, which is rotated by an external rotary plate, to provide bulk mixing in the remote ink tank.
It has been recognized, however, that a microfluidic dispensing device having a compact design, which includes both a fluid reservoir and an on-board fluid ejection chip, presents particular challenges that a simple agitation in a remote tank does not address. For example, it has been determined that not only does fluid in the bulk region of the fluid reservoir need to be remixed, but remixing in the ejection chip region also is desirable, and in some cases, may be necessary, in order to prevent the clogging of the region near the fluid ejection chip with settled particulate.
What is needed in the art is a fluidic dispensing device having a stir bar and associated structure that provides for both bulk fluid remixing and fluid remixing in the vicinity of the fluid ejection chip.